Digital techniques have become the circuit techniques of choice in electronic design. The high noise immunity of digital circuitry provides more reliability than analog circuitry. This stems from the binary nature of digital signals. Minor noise or component variations do not affect the information carried on a digital signal so long as they do not change a binary bit from a logical 1 to a logical 0 or vice versa. This provides a high degree of data integrity in digital circuitry.
On the other hand, problems which do cause the value of a binary bit to change (glitches) can cause errors which propagate throughout the circuit. A change in one bit in a digital number can drastically change the value of that number. Thus, although digital circuitry is more immune to error than analog circuitry, the errors that do occur can have more impact. Therefore it is very important to eliminate of mitigate all potential sources of glitches.
One common source of glitches is timing errors. Timing errors occur when signals arrive at the input terminals of a combinatorial circuit, such as a logic gate, at different times. The combinatorial circuit reflects to the combination of the old signal value of the slow signal with the new signal value of the fast signal. The combinatorial circuit then provides an output signal in response to the old and new signals when it should only provide an output signal in response to the two old signals and then the two new signals.
Most digital signals do not arrive at a combinatorial circuit at exactly the same time, but, in most circumstances this is not a problem. Either the combinatorial circuit does not react quickly enough to produce glitch output signal before the correct new signal is received or appropriate timing design assures that these glitches are lost in the system. However, in some asynchronous designs and capacitive discharge circuits, this type of glitch can cause errors or seriously impair proper operation of the circuit. Therefore it is important to eliminate these glitches in those types of circuits which are sensitive to them.